Delayed audible call signal for telephone substations



NW, 2L 195w s. B. KENT I 2,533,221 7 DELAYED AUDIBLE CALL SIGNAL FOR TELEPHONE SUBSTATIONS Filed Aug. 27, 1947 2 Sheets-Sheet 1 FIG. 3

JNI/ENTOR 5. 5. NEW? ATTORNEY av, l, H95@ 5, KENT 2531,21

DELAYED AUDIBLE CALL SIGNAL FOR TELEPHONE SUBSTATIONS Filed Aug. 2'7, 194'? 2 Sheets-Sheet 2 FIG. 5

lNl/ENTOR 5. 6. WE 1W A TTORNEV Patented Nov. 21, 1950 UNITED STATES PATENT OFFICE DELAYED AUDIBLE CALL SIGNAL FOR TELEPHONE SUBSTATION S Application August 27, 1947, Serial No. 770,795

6 Claims.

This invention relates to electric signaling and particularly to signaling facilities for use at telephone subscribers stations.

The signal equipment commonly used at telephone subscribers stations to indicate the arrival of telephone calls thereat consists of an electromagnetically operated device, generally characterized as a ringer, which responds to each application of ringing current to a subscribers line to produce audible signals of uniform in-- tensity. In some instances it has been found desirable to precede such an audible signal with a distinctively difierent type of preliminary call signal, usually in the nature of a visual signal of relatively low attention-arresting quality. It has been found desirable also in some installations involving preliminary visual and secondary audible signals to render the audible signaling device responsive to incoming signaling current onl in the event the preliminary call signal is not answered within a predetermined interval of time.

It is the object of this invention to provide an improved system of telephone signaling involving preliminary and secondary call signals at telephone subscribers stations,

ihis object is attained in accordance with a particular featureof the invention by the provision of novel subscriber-controlled means for variably delaying the operation of an audible signal device relative to the operation of a preliminary signal of the usual type. More particularly, the improved signaling facilities of this invention comprise a lamp signal which responds, as a preliminary visual Signal, to ringing current incoming over a telephone subscribers line; an audible signaling device which functions a predetermined interval of time after theresponse of the visual signal; light sensitive control means for enabling the audible signaling device at the termination of the predetermined time interval; and subscriber-controlled means for regulating the length of the predetermined interval of time.

- In accordance with another feature of the invention the light energy employed to activate the signal-enabling light-sensitive control means is derived from the preliminary visual signal.

A further feature of the invention resides in the use of means which precludes the possibility of lost calls at a subscribers station because of failure of the preliminary visual signal thereat.

These and other features of the invention will be readily understood from the following detailed description when read with reference to the accompanying drawings, in which:

Fig. 1 shows diagrammatically a telephone system of the full automatic type involving a, called subscribers station equipped with the signaling facilities of this invention;

Figs. 2 and 3 are illustrations of mechanical details involved in the subscriber-controlled means for regulating the time interval between preliminary and secondary signals and are taken along the lines 2 2 and 3-3 respectively of Fig. 1, looking in the direction of the arrows;

Fig. 4 is a circuit diagram of a portion of a subscribers line circuit and illustrates a modification of the facilities disclosed in Fig. 1; and

Fig. 5 is a circuit diagram illustrating a further modification of the invention shown in Fig. 1.

In the system illustrated in Fig. 1 a subscribers line AL, with which is associated the substation A, terminates at a central ofii-ce in terminals of the connector C. As previously indicated, the subscribers station is equipped with combined visual and audible signaling instrumentalities, the latter being in the form of the well-known electromagnetic telephone ringer indicated at Ill. The ringer it is connected across the secondary winding of transformer H0 in series with the main gap of a gaseous discharge trigger tube II which includes a cold cathode l2, an anode I3 and acontrol electrode Hi. As will appear more fully from a later description, ringing current from a source I l5 at a telephone exchange is impressed on the primary winding of transformer Hi3 and thence by induction on the transformer secondary across which the ringer l0 and the main gap of tube H are connected. The trigger tube ii will not fire on normal ringing current unless the control electrode I4 is made positive with respect to the cathode l2.

The visual signaling instrumentality consists of a gaseous discharge lamp I5 which is electrically bridged across the secondary winding of transformer ill) and physically housed within the left compartment I! of an effectively light-tight box it. The box it, which may be located in close proximity to the telephone at station A includes a dividing wall which separates the left compartment i? from a right compartment l8. At substantially its mid-section the dividing Wall of the box I 6 is apertured to provide a fixed support for a lens 59. The inner surfaces of the spacelimitin-g walls of the left compartment I! of box It are painted black in order that light rays entering a translucent window 2E located in the left wall of box it from external sources may be absorbed and thus precluded from influencing the photoelectric tube 2! housed in the right 3 compartment I8. To further prevent external light from reaching the phototube 2! the glass envelope of lamp !5 may also be painted black except for those areas which face the window 25 and the lens Hi. This painting of the lamp !5 is indicated by the numeral 22. The cathode 23 of lamp i5 is opaque and prevents any direct rays of light from window 28 reaching lens l9 and the tube 2!. When the lamp !5 is energized by ringing current incoming over line AL one side of the cathode 23 illuminates the window to provide a visual signal while light from the other side of the cathode 23 energizes phototube 2! under conditions and in a manner to be described presently.

The photoelectric tube 2| may be of any wellknown design and is suitably mounted in the right compartment !8 of the box !6. The cathode 2 3 of tube 2! is disposed in horizontal alignment with lens I9 and the cathode 23 of lamp I5 sothat when the lamp I5 is lighted the lens !9 for-ins an image of the cathode 23 of lamp I5 on the cathode 24 of phototube 2! In'ter-pos'ed between the lens !9 and the phototube 2 is an iris screen or shutter 25 of any wellknown design which functions to regulate the iamsunt of light which reaches the phototube 2! frointhe light source [5 through the lens [9. Through means, to be described presently, the iris shutter 25 may be adjusted from a fully closed position, at which no light from the source !5 reaches the phototube 2!, to a completely open 'p'os'itiom at which a maximum amount of light rays impinge on the cathode 2 3 of phototube 2!. When the iris shutter is completely closed the pho'totub'e 21' will not be activated even when lamp i5 is lighted. When the shutter is set wide openthe activation of the tube 2'! will be a maximum; As will be described hereinait'er the extent of the illumination of phototube 2! determines the rate at which condenser 25- charges and the time which elapses between the lighting of lamp !5 and the operation of ringer 10.

The" control of the iris shutter is effected by means of a manually rotatable knob 2'! which is mounted on the right extremity of a short shaft 21.; which is suitably housed in and projects from a circular aperture in the right vertical wall of the bo'x [6; A gear 29 is fixed to the inner end of shaft 28" and is in constant mesh with pinion shaft 3! carries a gear 32 which, as clearly shown I in Fig. 2, is in constant mesh with sectional gear 33- associated with the iris shutter 25. Rotation or the knob 28 in one direction from zero position causes the opening of the iris shutter to increase from zero to maximum. Any intermediate 'opening of the shutter may be obtained by setting the knob pointer or indicator 34 to any corresponding position on the dial 35. The dial may he graduated in delay indicia.

It will be observed that condenser 26 is connected across the secondary of transformer H0 in series with resistance 3'! and the space path of the phototube 2! and that the condenser controls the potential applied to the control electrode !4 of the trigger tube l l. The charge on condenser 25 is determined by the extent of the illumination of the phototube 2! and since the delay in firing trigger tube I is determined by the charge on condenser 26, the delay imposed on the operation of the ringer i0 is a function of the phototube 4 illumination. During the negative half wave of ringing current in the secondary of transformer Hi! the condenser 26 is charged to an amount dependent upon the illumination of tube 2!. During the positive half cycle the anode !3 of trigger tube I! is positive with respect to the cathode I2 and the tube will fire if the control anode i4 is sufficiently positive with respect to the cathode !2. The voltage on condenser 26 is trapped during the positive half wave and adds to the voltage drop across resistance 36 to render the control anode i l more positive. When, on successive alternations of ringing current the condenser 26 accumulates sufficient charge the potential on the control anode M will reach a value at whichthe tube I! fires. When the tube li fires the space path from anode !3 to cathode !2 is completed and the ringer I!) is energized on the incoming ringing current to give an audible signal. The herein described photoelectric control ofgas tube I? is a variation of the control system disclosed ina copending application, Serial No. 749,725, filed May 22, 1947, now Patent No. $481,667 issued September 13', 1-949, W. H. T.Holde1i.

Since the delay in firing trigger tube u and therefore, the operation or the audible signal it is, as previously stated, afunction of the illumination of phototube 2!, the lapse of time between the lighting of visual signal I5 and the operation of the ringer it may be controlled by regulating the amount of light from lamp !5 that is permitted to activate the phototube 2!. This regulating operation is subscriber-controlled and is performed through the media of the iris shutter 25 and the associated manually operable knob 21 in the manner hereinbc'fore described.

The system disclosed in- Fig. 1 operates in the following manner: For purposes of description it will be assumed that asubscriber at station B on line CL originates a callto the line AL which is allocated to the substation A at which there is located the dual signaling instrumentalities of this invention. The calling subscriber initiates the call in the usual manner and operates the dial H2to cause the extension of the line CL to the called line AL by way of automatic switches such as the schematically illustrated selector switch S and the connector switch When the connector C has been set on the terminals of the called line AL and has found the line to be idle relay H3 operates in the wellknown manner and locks over its upper winding and contact to the sleeve" conductor H4 which is grounded at this time. Relay l !3 closes the ringing circuit which may be traced from the generat'or H5, through battery I I6} interrupter Ill, lower front contacts or relay H 3, through the lower winding and lower back contact of tripping relay H8, inner lower front contact of relay H3 over the ring brush of connector C and its associated terminal, through the primary winding of transformer I Hiand condenser [20, and returning over the upper or tip terminal and associated brush of connector 0', cuter upper front contact of relay H3 toground at the outer upper back contact of relay H8. During the-ringing inter- Veil of interrupter I l alternating ringing current from the source 5 flows through the primary windin of transformer H0 and induces a corresponding voltage across the secondary winding thereof. The lamp !5- is energized by this voltage over an obvious circuit and furnishes a visual indication of the incomingcall at station A.

For descriptive purposes only it will be assumedthat the subscriber at station A has elected to have incoming calls indicated by a visual signal. only. In this case the knob 21 is operated to a position in which the iris shutter 25 is completely closed thus precluding the transmission of light rays from the lamp [5 to the phototube 2|. Obviously therefore, the phototube would never become activated and condenser 26 would not charge. The normal ringing current is incapable of firing the trigger tube and the ringer Hi would remain on open circuit with respect to the incoming signaling current. The ringer therefore would not function to audibly indicate the incoming call.

If the subscriber at station A had set the knob at some intermediate position, a definite amount of light from lamp l5, by way of lens It would become available to activate the phototube 2| with the result that the condenser 26 charges on successive negative half waves of ringing current until the charge thereon plus the drop across resistance 3% is sufficient to raise the potential of the control anode Hi of the trigger tube H to a value at which the tube I fires. When this occurs the energizing circuit for ringer I is completed and an audible signal sounded. The duration of the interval of time between the lighting of lamp l5 and the operation of ringer I!) is determined by the setting of the iris shutter 25. If the shutter had been positioned so that a maximum amount of light energy from lamp it was permitted to activate the phototube 2| the ringer 9 would operate substantially simultaneously with the lighting of the lamp l5.

Upon receipt of the signal indicative of the incoming call the'subscriber at station A removes the receiver from its support to complete the communication circuit to his substation equipment in the usual manner. A switchhook contact 228 is provided to short-circuit condenser 2t and thus silence the ringer iii or to prevent its operation if the receiver is lifted before the trigger tube H has fired.

When the called subscriber answers, as described, increased current flowing through relay H8 causes the relay to operate and lock over its upper winding and contact to grounded conductor IM. Relay H3 also removes ringing current from the connection and closes the tip and ring conductors through for communication purposes.

When the subscribers complete the conversation and restore the receivers to their respective supports, the automatic switches are released and all equipment is restored to its normal condition.

A variable resistance 38 may be connected in shunt of condenser 26 by operating switch 39 to its closed position and thus preclude charging of condenser 26 due to leakage of light from window around the cathode 23 of lamp it: through lens Hi to the phototube 20. The necessity for resistor 38 will be minimized by the leakage of electron flow from cathode E2 to control anode it of trigger tube on the positive half waves of ringing current without breakdown of the tube.

Fig. 4 illustrates a modification of the circuit disclosed in Fig. 1 and is intended to replace that portion of the latter contained within the broken lines a2--y. This modification precludes the possibility of lost calls which might otherwise occur because of failure of the glow lamp l5.

Under normal conditions, that is with lamp l5 in proper working condition the condenser 26 will sip charge as previously described to effect. the delay in the operation of ringer I0. However, if the lamp l5 of Fig. 1 fails to light, the ringer In would not operate and all calls incoming to station A would be lost. To avoid this possibility a thermistor it, a rectifier 4|, 9. slow-to-release relay 33 and a variable resistance d2 are added to the circuit of Fig. l as shown in Fig. 4. The thermistor may be of any well-known type which is designed to heat at a rate such as to give the maximum delay desired. Rectifier 4| serves to trap the charge on condenser 25 during positive half waves of ringing current, which charge is accumulated during the negative half waves. Thus when ringing current is impressed on the primary of transformer HQ, with the lamp l5 disabled, condenser 26 will charge through thermistor 4e and rectifier ii during the negative half cycles to eventually raise the potential of the control anode i i of trigger tube H to a value at which the tube H fires. When this occurs an obvious operating circuit for slow-to-releaserelay 43 is completed in which the relay operates. In operating, relay 'is connects the ringer It to the ringing circuit causing it to operate as an audible signal. Operation of ringer Iii without a previous visual indication of an incoming call indicates failure of the lamp l5.

In the modification shown in Fig. 5 the gaseous discharge lamp I5 and the phototube 2| of Fig. l are replaced by a double plate electrode cathode glow lamp 5t and a silicon photo-conductive device 5|, respectively. The glow lamp 56 which is a tube for the production of modulated light may consist of two parallel plane electrodes I and 2 placed in such close proximity that the discharge occurs between the outer surfaces of the electrodes instead of between the innor surfaces. When the electrode spacing and gas pressure are correct a uniform glow appears on the outer surface of the cathode. (A tube of this type is disclosed and described on page 450 of Theory and Applications of Electron Tubes, second edition, by Reich.) When ringing current is impressed on the transformer H0 in the manner previously described, plate I of the lamp 56 becomes the cathode on the negative half cycles and gives forth light to energize the photoconductive device 5| through the lens I!) causing condenser 26 to be charged in the manner previously described. On the positive half Waves electrode 2 becomes the cathode and is illuminated to furnish a visual signal at the window 20 of box It. At this time the electrode of tube '58 is dark so that the resistance of light sensitive cell 5| is increased to trap the charge on condenser 26. As in the case previously described when the accumulated charge on condenser 25 has reached a sufficiently high value the trigger tube H fires and completes the connection of the ringer W to the ringing current circuit. .ihe ringer then functions to give forth an audible signal. The iris shutter 25 is controlled by the subscriber in the manner hereinbefore described to regulate the quantity of light which reaches the light sensitive device 5|. As this quantity of light is increased or decreased at the will of the subscriber the period of delay in the operation of the audible signal is decreased or increased, respectively.

The light sensitive device 5|, per se, may take any suitable form. The fundamental requirement of the device is its capability of varying its electrical resistance inversely with the quantity of light to which it is exposed. A suitable device 7, of this character is disclosed in a copending application of G. K. Teal, Serial No. 655,695, filed March 30, 1946;

What is claimed is:

l. The combination in a telephone system of. a line, astation on said line, asource of signaling current, means connecting. said source to said line, a lamp at said station energized by current from said. source, a ringer at said. station, a time measuring condenser at said station, a charging circuit for said condenser including lightsensitive means adapted to be illuminated by light from said lamp, means at said station for regulating the illumination of said light sensitive means by the light from. saidsource to variably control. the charging time of said condenser, and means responsive to the charge accumulated on said condenser at the end of a predetermined interval of time for rendering said ringer responsive to current from said source.

2. The combination in a telephone system of a subscriber's line having a station thereon, a source of signaling current, means for connecting said source to said line, a light-emitting signaling device at said station energized by current from said source to provide a visual calling signal, an audible signaling device at said station, a condenser at said station for measuring a predetermined interval. of time following the connection of said source to said line, light sensitive means adapted to be illuminated by light from saidlight-emitting signaling device included in the charging circuit ofv said condenser, the rate at which said condenser is charged being commensurate with the amount of illumination of said light sensitive: means, manually operable means at said stationfor regulating the illumination of said light sensitive means, and means responsive. to the charge accumulated on. said condenser at the. end of a predetermined interval of time for rendering said ringer responsive to current from said source- 3, The combination in. a telephone system of asubscribers station, a source of alternating current, a lamp at saidstation, a ringer at said station and means for rendering said lamp and ringer responsive to current from said source in apredetermined timed sequence comprising a normally inert space discharge tube for connecting said ringer'to said source and having a controlelectrode, a condenser connected for charging to said source andpoledso as to apply a firing potential to the control electrode of said tube to cause said tube to fire and connect said ringer to said source, light sensitive means included'in the charging circuit-of. said condenser, and means for directing light from said lamp in variable amounts to said light sensitive means to variably control the charging time of said condenser.

4 A call signaling unit for use at a telephone subscribers station comprising in combination with a telephone line a light emitting signaling device. normally connected to said line, an audible signaling device normally on open circuit with respect to said line, means for connecting said audible signaling, device to said line, a photoelectric tube for controlling the operation of. said connecting means,, and means for focusing light emittedv from said. light emitting signaling; device onto said. photoelectric tube.

5. A. call signaling, unit for use at a telephone subscribers station comprising, in combination with a. telephone line, a light emitting signaling device normally connected to said line, an audible signaling device normally on open circuit with respect to said line, means for connecting said audible Signaling device to said line, a light sensitive device for controlling the operation of said connecting means, means for focusing light emitted by said light emitting signaling device onto said light sensitive device, and subscribercontrolled means for regulating thev extent to which light from said light emitting signaling device is focused on said light sensitive device.

6. A call signaling unit for use at a telephone subscribers station comprising in combination with a telephone line, a light energy emitting device normally connected to said line, a signaling device normally on open circuit with respect to said line, means for connecting said signaling device to. said line, a light sensitive device for controlling the operation of said connecting means, means. for directing the light energy of said light emitting device to said light sensitive device, and means for regulating the amount of light energy directed to said light sensitive device.

STANLEY B. KENT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,848,839 Ranger Mar. 8, 1932 1,860,007 Bascom May 24, 1932 1,901,919 McKee Mar. 21, 1933 2,084,267 Hicks June 15, 1937 2,186,542 Gloess Jan. 9, 1940 2,302,544 Halligan Nov. 17, 1942 2,428,007 Boardman Sept. 30, 1947 2,461,241 Shann Feb. 8, 1949 FOREIGN PATENTS Number Country Date 444,074 Great Britain Mar. 12, 1936 OTHER REFERENCES Serial No. 326,650, Danvillier (A. P. C.), pub. May 18, 1943. 

